Autoimmune conditions are characterized by the body attacking itself by mounting an immune response against self antigens to which it is normally tolerant. As such, approaches to treating autoimmune conditions, have focused on down regulating the “inappropriate” immune response against self. However, many approaches to treating autoimmune and like conditions are not specific to down regulating the immune system's response to a specific antigen. Rather, therapies focus on a general suppression of the immune system. Similarly, cancer can be characterized by increased expression of self oncogenes that are not adequately recognized by the immune system. As such, adjustment of the regulation of the immune system in regards to the identification of self antigens can be used to address both autoimmune conditions and cancer.
Some of these less antigen specific approaches utilize monoclonal antibodies that act on activated T cells and down regulate them such as by anti-CD3 (Protein Design Laboratories) or block APC and T cell interaction by anti-ICAM-3 (ICOS). MEDI-507 (Medimmune) is believed to be a humanized monoclonal antibody, for psoriasis that also targets CD2, presumably for removing or inactivating those cell types. Other diseases, such as, tissue transplantation rejection and allergies are also being tested by this approach. In contrast to acting on cell surface markers, rhu-mAB-E25 (Genentech) is believed to be a humanized monoclonal antibody against IgE that binds to circulating IgE, with the goal of preventing activation of mast cells. In contrast, other researchers are developing monoclonal antibodies to act on symptoms or agents directly causing disease symptoms. Remicade Infliximab (Centocor™) is purported to be a monoclonal antibody to TNF. Anti CD40 ligand has been used for treatment in animal model of multiple sclerosis (MS) (L. M. Howard, et al., 1999, J. Clin. Invest, 103:281). A recombinant generated designed protein Enbrel (Immunex™) is purported to comprise two molecules of r-DNA derived TNF receptor, and is intended to block TNF's action.
It should be noted, however, that many of these agents are not sufficiently disease specific and often recognize and could affect normal cellular and body constituents that have a defined and necessary role in normal immune defenses which are still needed.
Some more antigen or disease specific approaches are exemplified by the attempt to treat MS patients by oral administration of myelin proteins which have recently been reported; the same group of researchers is also using collagen type II for treatment of patients with rheumatoid arthritis. These treatments are designed to attack at the level of the gut associated lymphoid tissues (GALT) to induce tolerance by antigen specific suppression of the immune system. It is not know if these treatments use the intact protein or a hydrolyzate containing smaller peptides. See D. Hafler, et al. 1988, J. Immunol., 141:181; K. Wucherpfennig, et. al. 1990, Science, 248:1016; K. Ota, et al., 1990, Nature, 346:183; and H. Weiner, 1999, PNAS, 88:9161.
Several researchers are testing peptide based materials for treatment of autoimmune conditions. One approach uses peptide as immunogen, given orally in large quantities. The peptide represents a peptide sequence that is though to be the autoimmune epitope itself or a modified form which may also have altered binding or improved stability properties. By use of the peptide it is thought that either the normal peptide or an altered peptide ligand (APL) will bind to the T cell receptor (TCR) and induce a state of anergy since the multiple sets of bindings that would occur with antigen presentation with an antigen presenting cell (APC) do not occur (A. Faith, et al., 1999, J. Immunol., 162:1836; Soares, et al. 1998, J. Immunol., 160:4768; M. Croft, et al. 1997, J. Immunol., 159:3257; L. Ding, et al., 1998, J. Immunol., 161:6614; and S. Hin, et al. 1999, J. Immunol., 163:2363). Some of the approaches with APL include using related amino acids such a D amino acids (U. Koch, et al. 1998, J. Immunol., 161:421), amino acids with substituted side chains (R. DePalma et al. 1999, J. Immunol., 162:1982), methylene groups to replace peptide bonds in the peptide backbone (L. Meda, et al., 1996, J. Immunol., 157:1213) and N-hydroxyl peptides (S. Hin et al. J. Immunol., 163:2363).
The more antigen-specific approaches outlined above rely on using large amounts of antigens to desensitize a subject to the antigen. The possible drawbacks and consequences of the administration of large quantities of antigen include further undesirable and unpredictable immune responses. Peptide-based immunomodulators have the possible advantage of being a well-defined immunogen that would facilitate the generation of a safe and predictable response. However, safety is maximized by the use of small quantities of immunomodulators targeted to specific immune cells instead of the use of large quantities of an antigen introduced into the patient.
Few therapeutics are available as recombinant proteins that can modulate the immune system in active and antigen-specific capacity. Viral vector vaccines have been attempted to promote antigen-specific immunomodulation. However, problems are also associated with viral vector vaccines. One problem is the immune response induced against the vector itself. This induced immune response severely limits the number and frequency of subsequent injections/boosters that can be administered. Moreover, some adenoviruses have the potential for causing allergic conditions such as celiac disease. It is also known that many viral proteins, including some from HIV and HSV contain immunosuppressive epitopes. Viral proteins are also suspected as causative agents for other autoimmune conditions such as type 1 diabetes. Multiple Sclerosis (MS), Myocarditis, and Graves disease.
Another disadvantage in using a DNA-based or viral vector vaccines, including for autoimmune conditions, is the possibility of the vaccine DNA being integrated into the host's genome. One alternative is to conjugate a particular epitope to a carrier protein to avoid such incorporation into the genome. It is known within the art to use large carrier proteins such as Keyhole Limpet Hemocyanin (KLH), Bovine Serum Albumin (BSA), or Antigenics' heat shock proteins (HSP) couple/conjugated or incorporated with a virus protein.
Other options for peptide delivery of peptide epitopes include the use of synthetic biodegradable microparticles like Poly(lactide-co-glycolide) PLG with aggregated antigen. Still other delivery technologies for peptide antigens include AutoVac™ of Pharmexa. Other small molecule delivery technologies for peptides are Antigen Express's ‘li-key’ delivery, phage display and Multiple Antigen Presentation (MAPS) technologies (Rosenthal 2005 Immune peptide enhancement of peptide based vaccines Frontiers in Bioscience 1:478:482).
Many of the known approaches have the major disadvantage of using large, very immunogenic carriers. Moreover, patient populations requiring such therapeutics have usually been exposed to many of these same antigens during their lifetimes. Hence, and similar to vaccine vector delivery of antigens, clearance of the antigen can be so vigorous in the previously exposed host that no response will occur to the new antigen. On the other hand, a strong immune response may occur upon reintroduction of the vector. For example, in the case of the conjugate VP22 containing HSV-1 protein, the response may be undesirable given that a majority of adults have had one or more exposures to HSV-1 (Muran-yiova et al. 1991 Immunoprecipitation of herpes simplex virus polypeptides with human sera is related to their ELISA titre. Acta Virol, 35:252-9).
In regards to immune-based cancer therapies, cancer can have many causes that result in the uncontrolled growth of cells. One cause of cancers is the mutation or increased expression of oncogenes in cancerous cells. Oncogenes, like all genes, function to code for a protein that is synthesized by the cell. Often, cancers are caused by a DNA mutation that alters the regulation of expression of the oncogene or oncofetal gene or a DNA mutation that causes a change in the amino acid sequence of the oncogene itself. The alteration of regulation of an oncogene or oncofetal gene or a mutation in an oncogene or oncofetal can also affect the expression of other proteins in a cancerous cell. Cancerous cells can, therefore, have different levels of protein expression compared with surrounding healthy tissue. A change in the level of protein expression or the expression of mutated proteins on the surface of cancerous can be used by the immune system to direct an immune response to cancerous cells.
The proteins expressed on the surface of a cancerous cell can act as antigens for an immune response. However, most of the proteins expressed on the surface of cancerous cells are non-mutated self-antigens. Self antigens are usually ineffective in triggering an immune response since they are present in healthy as well as cancerous cells. Even in situations where a cancer cell is expressing a mutated protein, antigenic changes in cancerous cells that are created by individual point mutations may be too subtle from the standpoint of the immune system to trigger a significant immune response. Since cancer cells utilize essentially the same cellular proteins as healthy cells, cancer cells can often grow and survive without generating an anti-cancer immune response.
Peptides can have sufficient structure to be recognized with specificity by immunoproteins, such as antibodies, and by immune cells. That is, short peptides having from about 8 to about 30 amino acid residues have sufficient structure to bind to antibodies and serve as an antigen, epitope or other ligand for proteins involved in the activation of the immune system. However, short peptides often generate no or only a weak immune response when administered alone to a human or animal subject. Often, it is necessary to link or to introduce short peptides with larger proteins or biomolecules to serve as a carrier or an adjuvant to induce an immune response that will generate antibodies specific to the short peptide and to initiate an immune response to these short peptides.
There is a need for peptide-based immunomodulators having a well-defined immunogen to treat cancer that facilitates the generation of a safe and predictable anti-tumor response rather than a mixed response including an immune response to a carrier. There is also a need for the development of peptide-based immunomodulators, and the related need for the identification of peptides capable of being recognized by specific components of the immune systems and generating a specific type of directed immune response.